1. Field of the Invention
The invention relates to a method for the production of (N-organylaminoorganyl)- and (N,N-diorganylaminoorganyl)trioorganylsilanes from corresponding (triorganylsilylorganyl) halides and N-organyl- or N, N-diorganylamines, and (N-cyclohexylaminomethyl)trimethoxysilane and [N,N-bis-(N′,N′-dimethylaminopropyl)aminomethyl]triorganylsilane obtainable by means of this method.
2. Background Art
(N-organylaminoorganyl)- and (N, N-diorganylamino-organyl)triorganylsilanes can be produced at present by means of three different methods.
Aminoalkyl-substituted silicon compounds having an alkylene bridge containing at least three C atoms positioned between the nitrogen and the silicon atom are obtained by hydrosilylation of corresponding unsaturated amine compounds with organosilicon compounds containing hydrogen atoms bonded to the silicon atom. Any free NH groups present on the amine-containing olefin component must be blocked by protective groups before the hydrosilylation reaction in order to avoid undesired secondary reactions.
Furthermore, (aminoorganyl)silanes can be converted into substituted (N-organylaminoorganyl)- and (N,N-diorganylaminoorganyl)triorganylsilanes by nucleophilic substitution reactions with the aid of organyl halides. A disadvantage of this method is the tendency of the organyl halides to undergo uncontrolled multiple alkylations.
The method for the production of (N-organylaminoorganyl)- and (N,N-diorganylaminoorganyl)triorganylsilanes by means of the reaction of (haloorganyl)silanes with corresponding amines is economically more advantageous than the two abovementioned methods. In particular, the ready availability of (chloroalkyl)silanes, which are obtainable by means of photochlorination of alkylsilanes or hydrosilylation of corresponding halogen-substituted olefins with Si-H-containing compounds, and are used, for example, as intermediates for the synthesis of a multiplicity of organofunctional silanes, proves to be advantageous. Furthermore, in this procedure, it is possible to employ a large number of similarly readily available primary and secondary amines for the synthesis of the (N-organylaminoorganyl)- and (N,N-diorganylaminoorganyl)triorganylsilanes which permits a very wide range of use of the method and therefore economical product changes with existing industrial production plants.
British patent GB 686,068 A discloses (amino)-, (N-organylamino)- and (N,N-diorganylaminomethyl)- or (N,N-diorganylaminoethyl)triorganylsilanes. Furthermore, GB 686,068 A also describes a method for reacting corresponding (chloromethyl)- or (bromomethyl)triorganosilanes with ammonia or a primary or secondary amine at temperatures of at least 50° C. for the production of (aminoorganyl)-, (N-organylaminoorganyl)- and (N,N-diorganylaminoorganyl)triorganylsilanes. As a rule, the (chloromethyl)- or (bromomethyl)triorganosilanes were initially introduced into a flask or autoclave, depending on the boiling points of the amine compounds used, and heated to temperatures above 100° C., particularly 110-130° C. In the case of higher-boiling amines, (e.g. cyclohexylamine) the sequence of mixing was the opposite and the (chloromethyl)- or (bromomethyl)triorganosilanes were added to the heated amine. The reaction time was from 2 to 8 hours depending on the amine compound to be reacted.
The (aminomethyl)silane derivatives are prepared by the method described in German Laid-open application DE 18 12 564 A1, by reacting a (chloromethyl)- or (bromomethyl)silane derivative with ammonia or a primary amine. The reaction is effected at temperatures of 80 to 100° C. for a period of 2 or 3 hours, the amine having been introduced initially in its entirety, in a molar excess of 1:3.2 to 1:6.
The methods described in GB 686,068 A and DE 18 12 564 A1 have very long reaction times, e.g. several hours. The yields obtained are low. The products are not obtained in the required purity and have to be purified by a complicated procedure before their further use. For example, the products obtained by the method described contain large amounts of ionogenic chloride or bromide. Without purification, their industrial use is limited. They cannot be used, for example, in sealing compounds which are applied to metallic surfaces, due to considerably greater corrosion due to the halides present.
In particular, the hydrochlorides or hydrobromides of the amines used in the synthesis, or the hydrochlorides or hydrobromides of the desired compounds are considered here as chloride- or bromide- containing impurities. In this context, it was surprisingly found that mixtures of (aminomethyl)silanes and the abovementioned hydrochlorides or hydrobromides can lead in some cases to very exothermic decomposition of the desired compounds with breaking of the Si—C bond and formation of correspondingly N-methylated amines at relatively high temperatures, as are necessary, for example, during the production and also for the distillative purification of the desired compounds. The N-methylamines thus formed influence the course of the synthesis in an undesired manner. This effect appears to correlate with the basicity of the amine compound: the less basic the (aminomethyl)silane, the more readily does this decomposition reaction occur. For this reason and also from the point of view of safety, low halide contents of the (aminomethyl)silanes described here are necessary. Although a number of methods for the reduction of halide contents in alkoxysilanes are known and are based, for example, on the precipitation of the dissolved halide by addition of alkali metal or alkaline earth metal alcoholate salts (e.g. EP 0 702 017 A1, DE 693 06 288 T2, DE 195 13 976 A1), superstoichiometric amounts of the salts are required for simple and efficient reduction of the halide content, since the desired complete removal of halide cannot be achieved by stoichiometric amounts. Disadvantageously, however, all (aminomethyl)silanes investigated to date tend under these conditions, such as the simultaneous presence of free alcohols and strong bases, to undergo decomposition reactions, for example, the breaking of the Si—C bond already described above. An alternative method which is said to permit reductions of chloride contents in alkoxysilanes by introduction of ammonia is described in German Laid-Open Application DE 199 41 283 A1, but here (aminoalkyl)alkoxysilanes are explicitly excluded from the field of use thereof. Furthermore, the heating of the completely premixed solution of silane and amine, described in DE 18 12 564 A1, is questionable from the point of view of plant safety owing to the exothermic reaction of the two components.
It has now been surprisingly discovered that the decomposition of (aminomethyl)silanes takes place not only in the presence of hydrochlorides, or of alcohols and bases, but the presence of alcohols alone is sufficient to bring about the formation of corresponding N-methylamines. The N-methylated amine derivatives thus formed compete during the reaction with unmethylated amine still present for reaction with the (halomethyl)silane and finally lead to the formation of (N-methylaminomethyl)silanes, which cannot be separated from the desired compounds by distillation. In order to avoid this undesired secondary reaction, alcohols must be absent from the reaction mixture. If at least one of the organyl radicals on the silicon atom is an alkoxy group, only amines having a low water content may be used in the method, since otherwise alcohols are liberated by preliminary reaction of the silane with water present in the amine.